The use of antibodies to purified membrane proteins, along with enzymatic iodination and SDS-polyacrylamide gel electrophoresis, has been used to identify specific enzymes in the endoplasmic reticulum of rat liver. These enzymes include NADPH-cytochrome P450 reductase and one of several species of cytochrome P450. The former is a minor protein of the membrane whereas the latter is a major microsomal protein. The reductase is externally located and attached to the membrane by a hydrophobic tail of about 70 amino acids. The cytochrome P450, one of three we have observed in the membrane, is induced by phenobarbital and has a molecular weight of 44,000, as determined by SDS-polyacrylamide gel electrophoresis. This protein appears to be extremely hydrophobic and we are proposing to determine its amino acid composition. The next phase of the proposal will be to isolate additional microsomal enzymes in order to obtain antibodies to the proteins. These antibodies will then be used in a similar fashion as described above to identify other proteins in the SDS-polyacrylamide gel patterns. They will also be used in compliment fixation assays and for immuno-precipitation experiments designed to determine which protein bands in the SDS-gels are related to enzymatic activities, and to determine the location of these enzymes in the membrane. The eventual goal will be to develop a membrane model which includes both structure and function and to determine th universality of this model for other membranes of the liver subcellular organelles.